Research and development are being vigorously made on organic electroluminescence devices because they can emit light with high brightness even by low voltage driving. In general, organic electroluminescence devices each has one or more organic layers including a light emitting layer and a pair of electrodes sandwiching them therebetween. For light emission, they utilize energy of an exciton generated as a result of recombination, in the light emitting layer, of electrons injected from a cathode and holes injected from an anode.
For the light emitting layer of organic electroluminescence devices, fluorescent materials or phosphorescent materials are used and as these light emitting materials, metal complexes can be used. For example, U.S. Patent Application Publication No. 2008/297033, WO09/073,245, and WO08/109,824 describe iridium complexes containing a condensed-ring azole ligand.
It is the common practice to employ sublimation purification for the purification of materials to be used for organic electroluminescence devices. Various techniques have been proposed for improving the efficiency in sublimation purification. For example, Japanese Patent No. 3516671 describes tris(8-oxyquinolinolato)aluminum characterized by that it has an exotherm of 2 J/g at a temperature between 350 to 400° C. in differential scanning calorimetry under nitrogen flow and has an endotherm of from 70 to 120 J/g at a temperature between 400 to 450° C. with a temperature near 420° C. as an endothermic peak. Japanese Patent No. 3525034 describes a technique of performing sublimation purification of an organic compound at a temperature lower by at least 30° C. than the thermal decomposition temperature thereof. Japanese Patent Laid-Open No. 11/171,801 describes a sublimation purification method of an organic compound including stirring or vibrating the organic compound.